The invention relates to an absorbent structure formed on the basis of particulate, superabsorbent polymer materials, where the superabsorbent polymer materials are bonded together by a lower-melting thermoplastic polymer. The invention relates furthermore to a method for producing an absorbent structure of this kind and a hygiene article having such an absorbent structure as an absorbent core layer.
When an absorbent structure on the basis of superabsorbent polymer materials is mentioned, this is understood to mean a structure having an amount of more than 70% by weight of superabsorbent polymer materials. It is in line with established understanding and established practice in the sphere of interest here of absorbent structures that superabsorbent materials are meant to refer to such materials which by absorption or gel formation are able to absorb and permanently retain at least about ten times their own mass in fluid. The fluid is bonded into the molecular structure of these materials and not simply absorbed into pores in the materials, from which it could be squeezed out again. Current superabsorbent materials are water-insoluble, cross-linked polymers which are capable of absorbing aqueous fluids and body exudates such as urine or blood by swelling and forming hydrogels and permanently retaining the quantity of fluid absorbed at least under a certain surrounding pressure.
It has been shown that absorbent core structures with such a high content, more than 70% by weight, of superabsorbent polymer materials (SAP) cannot be realized using traditional fiber-based structures, because the particulate SAP materials cannot be arranged to be sufficiently accessible on the one hand and not be sufficiently immobilized on the other hand.
From DE-A-2 222 780 it is known to apply the particulate superabsorbent polymer materials on an underlayer together with particles of a thermoplastic material to produce an absorbent structure formed on the basis of superabsorbent polymer materials and then to melt the thermoplastic material to obtain a composite.
A structure of this type of superabsorbent polymer materials and thermoplastic polymers was not successful in practice, because the accessibility of the superabsorbent materials for the impinging fluid was not sufficiently ensured. Moreover, this structure proved to be too rigid and was consequently characterized by insufficient comfort for the wearer.
The production of an open-cell polypropylene foam with a pore content of more than 20% by volume is known from WO 94/13460. Packaging and the use of the foam for sound absorption and thermal insulation are named as areas of application.
The production of an extruded thermoplastic foam is also known from WO 98/56430. The foam preferably has a structure consisting of cell walls and cavities. The foam can be used, according to the description, as the container for a piece of meat or a layer in a diaper.
The object of the invention is to eliminate the aforementioned disadvantages in the case of an absorbent structure of the generic type named at the beginning having a high SAP content, that is, to achieve a flexible structure having good fluid absorption and retention characteristics, which can also be manufactured simply.